APES 4.9 El Nino and La Nina

• ENSO (El Nino - Southern Oscillation) is a regular event that occurs every 3-7 years, beginning in December
• ENSO takes place in the southern Pacific Ocean, between Australia and South America
• Changes in atmospheric winds and ocean currents play a part in ENSO, and it effects associated terrestrial areas
• Normal wind patterns blow from east (South America) to west (Australia)
    * These are the easterlies/easterly trade winds
• During El Nino, winds stall
    * They may reverse and become westerlies
    * The position of cloud formation also changes as warm air is rising in a different place
• La Nina is an “enhanced normal”
    * The easterlies are stronger
    * More moisture is driven into the atmosphere
• In normal conditions, as cold water rises up to the coast of South America, bringing with it lots of nutrients
    * Fish that feed on these nutrients are drawn to these upwellings and thrive off the coast during this time
    * But when the winds and currents stall/reverse, that upwelling isn’t as prominent, and so fish populations migrate or decline
    * Note the economic impacts this will have on South American fishing industries
• La Nina will have warm water traveling closer to the Australian coast and an intensified upwelling

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